Open Data supplied by Natural Environment Research Council (NERC)

Niskin Bottle

The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.

Standard Niskin

The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.

Lever Action Niskin

The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.

Clean Sampling

A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.

Deployment

Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles have a capacity between 1.7 and 30 L, while Lever Action bottles have a capacity between 1.7 and 12 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

D233 Discrete CTD Inorganic Nutrient Sampling Document

Originator's Protocol for Data Acquisition and Analysis

Sample collection and analysis

Discrete dissolved inorganic nutrient samples were collected from Niskin bottles fired on 139 CTD casts performed during D233. Samples were collected in 30 ml plastic diluvial sample cups, each washed three times in the sample flow. Samples were stored in a 4 °C fridge (duration between 1 and 12 hours) prior to onboard analysis. 8 ml subsamples were drawn into sample cups and run on the SOC Chemlab AAII-type Auto-Analyser connected to a digital-analysis microstream data capture and reduction system. Duplicates were analysed (where possible) to ensure accuracy and to increase precision.

Primary standards were prepared in calibrated 500 ml glass volumetric flasks (calibrated polyethylene volumetric flasks for silicate), two standard solution for each nutrient being required for the cruise. These utilised pre-weighed salts measured prior to the cruise. Sets of working standards were typically made up from these on a daily basis in 100 ml calibrated polyethylene volumetric flasks, using artificial seawater (40 g/l NaCl). These were run in duplicate prior to each analytical run to enable sample calibration. Independent quality control samples were also prepared from standard solutions supplied by OSI and run (in duplicate) at intervals throughout the analysis.

The cruise report contains more in depth details of each nutrient analysis performed during the cruise.

BODC Data Processing Procedures

PSTAR-formatted CTD sample data collected on the cruise were supplied to BODC during December 1999. The inorganic nutrient data were extracted from these files and loaded into BODC's Oracle database. Flags were assigned if values were considered suspect.

Content of data series

Originator's Parameter

Unit

Description

BODC Parameter code

BODC Unit

Comments

SiO 3

µmol/l

Concentration of silicate per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis

SLCAAATX

µmol/l

No unit conversion necessary

NO 2 +NO 3

µmol/l

Concentration of nitrate+nitrite {NO3+NO2} per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis

NTRZAATX

µmol/l

No unit conversion necessary

PO 4

µmol/l

Concentration of phosphate per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis

VIVALDI, a seven year programme of seasonally repeated surveys to study the upper ocean.

Long-term observations of ocean climate in the North West Approaches.

Satellite ocean surface topography, temperature and wind data were merged with in situ observations and models to create a complete description of ocean circulation, eddy motion and the way the ocean is driven by the atmosphere.

The surveys were forerunners to the international Global Ocean Observing System (GOOS). GOOS was later established to monitor annual to decadal changes in ocean circulation and heat storage which are vital in the prediction of climate change.

Please note:the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.